The research encompassed within this Program Project is organized around our hypothesis that physiological gene therapy for sickle cell disease may be achieved by genetically reversing the switch from fetal (HbF) to adult (HbS) hemoglobin through gene transfer into hematopoietic stem cells. Our goals are to achieve a growing understanding of the molecular mechanisms that control red cell formation, the regulatory factors that determine the proportion of gamma and beta-globin gene expression and the biological controls that modulate stem cell behavior and transduction. In Project by Ihle, "Signaling by the Epo Receptor in Erythropoiesis", the proposed research seeks to understand the mechanisms by which the EPO receptor signals via a Jak2 independent pathway in activating the N-myc promoter. Epo receptor mutants will be evaluated in transgenic mouse models expressing the human beta-globin locus to evaluate the potential role of signaling pathways emanating from the Epo receptor on hemoglobin switching. In Project by Cunningham, "Identification and Characterization of Factors Which Modulate gamma-Globin Gene Expression", experimental efforts are focused on understandlng the role of the stage selector protein (SSP), on the gamma to beta switch using biochemical methods and transgenic mouse models. In Project by Sorrentino, "In Vivo Selection of Transduced Hematopoietic Stem Cells", a selection system based on a variant methylguanine, methyltransferase gene and the effect of HOXB4 on stem cell renewal will be evaluated in a rhesus model. Factors which may contribute to transformation by vector insertional mutagenesis will be evaluated in tumor prone and immunodeficient mouse strains. In Project by Nienhuis, "Gene Transfer Into Hematopoietic Stem Cells", lentiviral vectors have been used to achieve gene transfer into stem cens in the rhesus model and to express globin genes in murine models of human hemoglobin disorders. Experiments are proposed to achieve high level gene transfer into steady state bone marrow cells, to evaluate globin therapeutic vectors in the rhesus model and to test the safety of globin gene vectors. This research is supported by an Administrative CORE and three scientific COREs that provide purified stem cells, standardized vector preparation and novel reagents for generation of vectors or access to unique animal models.